电解质浓度和对称性对电门控纳米通道中表面非均匀电荷的影响
Effect of electrolyte concentration and symmetry on the heterogeneous surface charge in an electrically gated nanochannel
摘要：
本研究的目的是探讨利用场效应诱导异质表面电荷，从而改变流体在具有收敛-发散周期性的固态纳米通道中的流动。它示出的几何形状和施加的栅极电压（V_{G}）的组合将产生异质表面电荷在沟道壁，可以由V_{G}调制，即，一个温和的V_{G}（0.7-0.9 V）导致电荷反转在发散部分的沟道，而V_{G} > 0.9使电荷反转在整个沟道中，但它仍然是不均匀的每个部分。结果表明，Zeta（Zeta）电位是V_{G}的函数，由于电解质的稀释，Zeta（Zeta）电位呈现线性到非线性的转变，这与密度泛函理论和蒙特卡罗模拟一致.相反，电解质的对称性有一个微小的影响的变化的反电势。还示出了通过稀释电解质和使用具有较低价态的更对称的电解质，跨沟道的跨沟道电位差（Δ Δ η）增加。第一次证明了在V_{G}中Δ ε呈现极大值。对应于最大Δ ε的V_{G}随着电解质的稀释和较高的阴离子价态而减小。这对于克服场效应射流器件的漏电流问题具有重要的实际意义。它还表明，速度场可以通过改变电解质浓度和对称性来改变。然而，应用VG被发现是比电解质改性更有效的方式。这包括在通道内产生循环，这对于混合或分离/捕集等应用至关重要。
英文摘要：
The present study aims to investigate utilizing field-effect for inducing heterogeneous surface charge and consequently changing the fluid flow in a solid-state nanochannel with converging-diverging periodicity. It is shown that the combination of geometry and applied gate voltage (V_{G}) would generate heterogeneous surface charge at the channel walls which can be modulated by V_{G}, i.e. a moderate V_{G} (0.7-0.9 V) causes charge inversion in diverging sections of the channel while V_{G} > 0.9 enables charge inversion in the entire channel but it is still non-uniform in each section. The results show that zeta (ζ) potential is a function of V_{G} which shows a linear to non-linear transition due to dilution of electrolyte in agreement with density functional theory and Monte Carlo simulations. In contrast, electrolyte symmetry has a minor effect on the variation of ζ potential. It is also shown that the difference in ζ potential across the channel (Δζ) increases by dilution of electrolyte and utilizing a more symmetric electrolyte with lower valances. For the first time, it is shown that Δζ presents a maximum with the V_{G}. The V_{G} corresponding to the maximum Δζ decreases with both dilution of electrolyte and higher anion valance. This is of practical importance to overcome leakage current problem of field-effect fluidic devices. It is also shown that the velocity field can be altered by changing both electrolyte concentration and symmetry. However, applying VG was found to be a more efficient way than electrolyte modifications. This includes generating circulation inside the channel which is of prime importance for applications such as mixing or separation/trapping.
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